One powerful approach to understanding human disease processes is to identify mutations that cause the disease in rare families, and explore how those causative mutations alter biochemical features of the protein. We examined a family from Iowa with a history of cerebral amyloid angiopathy, a disease of amyloid deposition in the cerebrovasculature which leads to hemorrhagic strokes. In most cases, this amyloid is composed of the Abeta peptide, which is a proteolytic fragment of the amyloid precursor protein (APP). We detected a previously unidentified mutation in APP which co-segregated with the disease. The mutation, which causes an amino acid change of aspartate to asparagine, was immediately adjacent to the previously identified "Dutch" mutation for CAA, which causes a similar amino acid change of glutamate to glutamine. This novel mutation marks the third residue of Abeta that causes familial CAA. In this R03 proposal, we will examine several aspects of the biochemistry of the mutant APP and mutant Abeta. In aim 1, we will test whether this mutation affects the processing of APP in both neuroblastoma cells and smooth muscle cells. We will measure secreted forms of APP, C-terminal fragments, and isoforms of Abeta. We will also analyze whether mutant APP interacts with the low density lipoprotein receptor-related protein (LRP). In aim 2, we will test whether the mutation affects the fibrillogenic character of Abeta. Specifically, we will examine the form of Abeta fibrils by electron microscopy and the rate of Abeta fibrillogenesis by thioflavin T binding. We will examine whether mutant Abeta fibrillogenesis is altered by binding proteins (apoE, apoJ) and cations (calcium, iron) and test whether Abeta exhibits altered toxicity towards smooth muscle cells in vitro. Through these various assays, we hope to identify processes that are altered in the mutant APP, leading to future proposals at understanding important factors in sporadic CAA.